Method of constructing substantially circular cross-section vessel by welding

ABSTRACT

A multi-layer, thick wall, substantially circular cross-section metal vessel includes a plurality of concentric tubular layers formed by the progressive deposition of molten weld metal mainly provided by electroslag welding process to form continuous helical strips with the axially adjacent convolutions of each helical strip being contiguous. The several helical strips are formed simultaneously, and each helical strip is solidified in contact with solidified metal. Each strip of molten metal forming a tubular layer of a relatively larger diameter is deposited progressively and progressively solidified onto a tubular layer of smaller diameter with an axial offset corresponding to a predetermined pitch of a helix.

United States Patent Ujiie [45] May 23, 1972 54] METHOD OF CONSTRUCTING3,223,818 12/1965 Chyle ..219/73 SUBSTANTIALLY CIRCULAR CROSS- ,5056/1964 Kirschnin /76 X SECTI N S BY rELD 1,533,300 4/1925 Baker 219/76 0VE I 2,299,747 10/1942 Hatter 219/76 [72] Inventor: Akira Ujiie,Kobe-shi, Japan 2,433,966 l/l948 Van Keuren.. ..29/474.l [73] Assignee:1hjlitlfubislhi Jukogyo Kabushiki Kaisha, Primary Emmi-MP4. Truhe 0 apanAssistant Examiner-J. G. Smith 22 Filed: Jan. 23, 1970 Attorney-WWW andToren [2]] Appl. No.: 5,311 57 ABSTRACT I A multi-layer, thick wall,substantially circular cross-section [30] Apphcauon Pnomy Dam metalvessel includes a plurality of concentric tubular layers Jan. 31 1969Japan ..44/6624 firmed by Pmgressive depsifin 0f Weld mainly provided byelectroslag welding process to form con- 1 7 2 5 tinuous helical Stripswith the axially adjacent convolutions of E 5 2 each helical strip beingcontiguous. The several helical strips [58] Fieid 29/474 are formedsimultaneously, and each helical strip is solidified 29/473 18 incontact with solidified metal. Each strip of molten metal forming atubular layer of a relatively larger diameter is deposited progressivelyand progressively solidified onto a tu- [56] References cued bular layerof smaller diameter with an axial ofiset cor- UNITED STATES PATENTSresponding to a predetermined pitch of a helix.

3,024,349 3/ l 962 Hinrichsen et al ..2 1 9/73 5 Claims, 4 Drawingfigures Patented May 23, 1972 3,665,143

INVENTOR ATTORNEY METHOD OF CONSTRUCTING SUBSTANTIALLY CIRCULARCROSS-SECTION VESSEL BY WELDING BACKGROUND OF THE INVENTION Recentlyconstructed vessels, used in various fields of industry, have beendesigned for use at very high temperatures and very high pressures, andalso for greatly increased capacity. This has necessitated that thesevessels be constructed with thicker walls, larger diameters and greaterlengths.

In order to satisfy these requirements, there has been developed amethod by the same inventor wherein a vessel of tubular cross-section orthe like is constructed solely from deposited weld metal by successivelydepositing molten weld metal mainly provided by electroslag weldingprocess to form a continuous helical strip, with the freshly depositedmolten weld metal being progressively deposited along, and progressivelysolidified in contact with already solidified metal. In this knownmethod, a thick-wall vessel, having a seamless wall, can be formedeasily and at a relatively low cost. The wall of such a vessel has agreatly decreased amount of non-metallic inclusions and has uniformmechanical properties.

However, as the wall thickness of the vessel increases, the known methodmay have the disadvantage that blowholes, cracks, and distortion arecaused by coarsening of the grain structure, especially at the time offormation of the thicker wall, by weld depositing a great amount ofmolten weld metal in one continuous step in order to increase depositionrate. Additionally, as a thick wall is deposited and solidified in onecontinuous step in the direction of the thickness of the wall, it isimpossible to make a wall, composed of different metallurgicalcompositions, so as to have appropriate properties at each respectivesubdivision of its thickness in a thick wall vessel, in the direction ofthickness, to meet the use requirements of the vessels.

SUMMARY OF THE INVENTION This invention relates to the formation ofmulti-layer, thickwall vessels by welding and, more particularly, to anovel method of and apparatus for such formation and which is free ofthe disadvantages of the prior an methods in the case of promotingefficiency of deposition rate.

More specifically, in the method of the present invention, a compositetubular vessel is formed solely from molten weld metal, by successivelydepositing molten weld metal to form a continuous helical strip, withthe freshly deposited molten weld metal being simultaneously andcontinuously deposited along, and solidified in contact with, the endconvolution of each stepped portion of already solidified metal having astepwise changing thickness. With the present invention, it is possibleto construct a vessel solely from deposited weld metal and free fromblowholes, cracks, distortion and coarsening of grain structure,

As molten metal is simultaneously and continuously deposited andsolidified in the form of a helix onto the end convolution of eachstepped portion of already solidified metal having a step-wise changingthickness, it is possible greatly to narrow the width of the depositedweld bead and the width of the solidifying weld bead, by dividing thevessel into several layers radially thereof. In addition, it is possibleto prevent the formation of blowholes to a great extent by decreasingthe temperature differences between the external and internalperipheries of the molten weld metal helices. Furthermore, because ofthe narrow width of the deposition and solidification of molten weldmetal, the chemical composition of each deposited weld metal layer isuniformly distributed, its structure is compact and the crystallizationdirection is stabilized, thus eliminating the formation of cracks anddecreasing distortion.

It is also possible to form a vessel having excellent proper ties byappropriately selecting the composition of the molten weld metal to bedeposited along and solidified with the end convolution of each steppedportion of the wall.

Apparatus embodying the invention includes a frame having a basic shapesubstantially the same as that of an end portion of the tubular body tobe formed by depositing molten weld metal, and having an end formedstep-wise in the direction of its radial thickness. The apparatus alsoincludes a driving means to rotate the frame about its axis, and aslidable strap in contact with the frame or with a metal zone depositedand solidified on the frame. Furthermore, a welding apparatus isincluded to supply molten weld metal successively to a plurality ofrecesses formed by the frame, or by a stepped surface of a metal zone,and by the slidable strap. The method of the invention can be performedvery easily, reliably and effectively by the apparatus of the invention.

An object of the invention is to provide an improved method of andapparatus for forming a composite tubular metal vessel solely bydeposited weld metal.

Another object of the invention is to provide such a method andapparatus adapted to form the vessel as a multi-layer, thick-walltubular vessel.

A further object of the invention is to provide such a method andapparatus for forming a composite metal vessel by welding and with whichthe vessel is free of blowholes, and cracks, caused by coarsening of thegrain structure and distor tlon.

Another object of the invention is to provide such a method andapparatus in which the weld metal is deposited in the form of aplurality of simultaneously deposited helical beads which are relativelynarrow both axially and radially of the vessel.

A further object of the invention is to provide such a method andapparatus in which axially successive convolutions of each helical stripor bead are deposited in axially contiguous relation.

A further object of the invention is to provide such a method andapparatus in which the helical strips or beads have different respectiveradii with each helical strip or bead being radially contiguous with anadjacent helical strip or bead.

Another object of the invention is to provide'such a method andapparatus in which radially adjacent helices are stepped progressivelyfrom each other, in a direction axially of the vessel being formed, bythe pitch of a helix.

For an understanding of the principles of the invention, reference ismade to the following description of a typical embodiment thereof asillustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a front elevation view of one form of apparatus forconstructing a composite vessel, by welding, in accordance with thepresent invention;

FIG. 2 is a part horizontal plan and part horizontal sectional viewtaken along the line IIII of FIG. 1;

FIG. 3 isan elevation view taken along the line III-III of FIG. 1; and

FIG. 4 is a view taken in the direction of the arrow IV of FIG. 2, witha water cooled copper strap being omitted.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, inthe illustrated embodiment of the invention, an electro-slag weldingprocess is used. However, it should be understood that other electricwelding processes are equally applicable.

The apparatus of the invention includes a cylindrical starting block 1whose right end is constituted by an inner or core tube la, anintermediate tube 1b and an outer tube 10. The end surface la of inneror core tube In is formed helically, and the ends of the helix adjoin ina radial plane la" with a step offset having a length p in the axialdirection, the length p representing the pitch of the helix. The endsurface lb of the intermediate tube lb, and the end surface 1c of theouter tube 1c, also are formed helically, with the ends of each helixabutting, in step formation, at the radial planes lb" and 10'',respectively, each including a stepped offset having the length p in theaxial direction.

A carriage 2 supports cylindrical starting block 1 for rotation about ahorizontal axis, and serves to retract block 1, in the actual direction,by the helical pitch distance p during each rotation of starting block1.

A water-cooled copper strap 3 has a stepped edge for close conformancewith the helical end surfaces la, 1b and 1c, and with the peripheralsurfaces 1a", 1b' and 1c of the respective tubes In, lb and 10. Copperstrap or block 3 also is formed to engage the inner peripheral surface1d of starting block 1.

Depressions or recesses A, B and C are formed on the respectiveperipheral surfaces la", lb" and 1c". Metallic welding materials 5a, 5band 5c, in the form of wire, rods, or strips, are wound on respectivereels 4a, 4b and 4c, and are fed to recesses A, B and C by respectivefeeding means 6a, 6b and 60. Reference numeral 8 indicates a powersource for a welding transformer which supplies welding current to themetallic weld materials 5a, 5b and 50 to respective electric contactbrushes or rollers 7a, 7b and 7c.

The operation of the illustrated apparatus will now be described. Whenthe ends of weld materials 5a, 5b and 5c are inserted into respectiverecesses A, B and C, a fixed quantity of flux is introduced into theserecesses, and power source 8 for a welding transformer is activated,electric current flows between the ends of weld materials 5a, 5b and 5cand the respective peripheral portions la", lb" and 1c" of startingblock 1, within the depressions and through the welding flux. The fluxis melted to form molten slag, and melting of weld materials 5a, 5b and5c is initiated.

When such melting is initiated, starting block 1 is rotated by carriage2 in the direction of axial descent of the peripheral surfaces la, lb"and 1c" of starting block 1, which is in the clockwise direction asviewed in FIG. 3. Simultaneously, block 1 is retracted axially by adistance equal to the helical pitch p during each complete revolution.During this rotation and retraction of block 1, molten weld metal fromthe respective weld materials 5a, 5b and 50, within the depressions A, Band C, is solidified onto the respective peripheral surfaces 1a", lb"and 1c of starting block 1, and deposited progressively on alreadysolidified molten weld metal to form helical strips. Thereby, tubularvessels, which have not been shown, are simultaneously formed at theright hand end of block 1 as illustrated in FIG. I, and the ends of theformed vessel have the same shape as that of the tip or right hand endof starting block 1.

As mentioned above, a thick-wall tubular vessel is divided into threeparts in the radial direction, and thus the radial width of each stripof molten weld metal can be decreased to one-third the overall thicknessof the vessel. As a result, at the time when the molten weld metal isdeposited and solidified, the temperature difference between the outerperiphery and the inner periphery of the tubular vessel can be greatlydecreased. Therefore, pipeJike blowholes, frequently occurring in theinteriors of molten ingots and the like, can be eliminated.

Because of the narrow width of the molten weld metal strips, thechemical compositions and the distribution of the grain structure areuniform, the crystallization direction is stabilized, and there are nowelding defects such as cracking and the like. Furthermore, the amountof weld metal deposition from each welding material is decreased toone-third, as compared with single-layer welding, and thus distortionpropor tional to the amount of deposited weld metal is significantlydecreased. As the weld materials are solidified at three pointssimultaneously, tubular vessels can be formed more effectively than inthe case of three separate weld deposition operations to form singlelayers during each deposition, and in succession.

The inner layer, the intermediate layer and the outer layer of theformed vessel, at the inner tube 10, intermediate tube lb and outer tube1c, respectively, of starting block 1, in the extended direction oftheir axes (not shown), are reheated by the melting heat resulting fromthe weld material to be solidified after the first revolution. Thereby,the effects of normalizing and tempering, similar to those obtained inthe case of heat treatment used in multi-layer welding at weldingjoints,

are present in the present invention method and apparatus. Especially,enhancement of nonnalizing and tempering effects can be effected in theinner layer and in the intermediate layer of the vessel, due,respectively, to the subsequently deposited intermediate layer and outerlayer of the vessel.

By utilizing a corrosion resisting metal for the inner layer weldmaterial 5a, a metal having high strength at a high temperature for theintermediate weld material 5b, and heat-resisting metal for the outerweld material layer 50, the end product will have a very high corrosionresistance against a corrosive material to be contained in the formedtubular vessel, and can adequately endure high temperatures and highpressures when these are applied to the outer surfaces of these vessels.

For example, in the case of reaction towers used in petroleum refiningand whose interior surfaces are exposed to hydrogen at high temperatureand high pressure to effect desulpherization, the partial pressure ofhydrogen at the wall of the reaction tower is nearly proportionallydecreased radially of the wall from the innersurface to the outersurface, and hydrogen tends to escape into the atmosphere. By usingappropriate materials having good resistance to corrosion by hydrogen,in a step-wise manner radially of the wall from the inner surface to theouter surface to match the respective partial pressures of hydrogen, theamount of expensive material,

having a high resistance to hydrogen corrosion, can be reduced, and thusthe manufacturing cost can be substantially reduced.

In the embodiment of the invention selected as an example, the number oflayers to be welded is three but, by increasing the number of layers,vessels having a better structure can be obtained as well as vesselshaving a wall of greater thickness. Also, while welding has beendescribed as performed successively from the innermost layer to theoutermost layer, it is possible to perform the welding in a reverseorder, that is, from the outermost layer to the innermost layer.

Also, in the exemplary embodiment, the formation of the vessel isperformed by rotating the cylindrical starting block 1 about ahorizontal axis. It should be understood, however, that it is possibleto perform the embodiment of the invention by utilizing the helicalpitch p and making the tubular starting block 1 to coincide with thethickness of the helical layers to be deposited and by rotating thestarting block 1 about a vertical axis. Finally, while an .electro-slagwelding process has been described as applicable in practicing theinvention, it is equally possible to employ MIG welding, TlG welding, ora submerged arc welding process.

While a specific embodiment of the invention has been shown anddescribed in detail to illustrate the application of the principles ofthe invention, it will be understood that the invention may be embodiedotherwise without departing from such principles.

What is claimed is: I

l. A method of forming a composite metal vessel solely of deposited weldmetal, comprising the steps of simultaneously and progressively welddepositing a plurality of strips of molten metal along and insolidifying contact with respective helical surfaces of solidifiedmetal; utilizing the deposited strips to form, simultaneously, aplurality of helices of deposited weld metal; depositing axiallysuccessive convolutions of each helix in axially contiguous relationwith each other; forming the helices with different respective radii andwith each helix radially contiguous with an adjacent helix; and steppingradially adjacent helices progressively from each other in a directionaxially of thehelices.

2. A method of forming a composite metal vessel, as claimed in claim 1,including forming the molten weld metal by an electro-slag weldingprocess.

3. A method of forming a composite metal vessel, as claimed in claim 1,including depositing the molten weld metal to form radially successivetubular layers of metal in which the strip of molten metal for eachtubular layer of a larger diameter is progressively deposited andsolidified onto the radially inner tubular layer of smaller diameter.

4. A method of forming a composite metal vessel, as

pitch.

5. A method of forming a composite metal vessel, as claimed in claim 1,including depositing said helical strips with radial and axialdimensions which are a minor fraction of the claimed in claim 3,including starting successive helices at 5 finalradialthickness ofthedeposited weld metal respective points offset axially by a predeterminedhelical

1. A method of forming a composite metal vessel solely of deposited weldmetal, comprising the steps of simultaneously and progressively welddepositing a plurality of strips of molten metal along and insolidifying contact with respective helical surfaces of solidifiedmetal; utilizing the deposited strips to form, simultaneously, aplurality of helices of deposited weld metal; depositing axiallysuccessive convolutions of each helix in axially contiguous relationwith each other; forming the helices with different respective radii andwith each helix radially contiguous with an adjacent helix; and steppingradially adjacent helices progressively from each other in a directionaxially of the helices.
 2. A method of forming a composite metal vessel,as claimed in claim 1, including forming the molten weld metal by anelectro-slag welding process.
 3. A method of forming a composite metalvessel, as claimed in claim 1, including depositing the molten weldmetal to form radially successive tubular layers of metal in which thestrip of molten metal for each tubular layer of a larger diameter isprogressively deposited and solidified onto the radially inner tubularlayer of smaller diameter.
 4. A method of forming a composite metalvessel, as claimed in claim 3, including starting successive helices atrespective points offset axially by a predetermined helical pitch.
 5. Amethod of forming a composite metal vessel, as claimed in claim 1,including depositing said helical strips with radial and axialdimensions which are a minor fraction of the final radial thickness ofthe deposited weld metal.